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Journal ArticleDOI

Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer

02 Jul 2001-Applied Physics Letters (American Institute of Physics)-Vol. 79, Iss: 2, pp 156-158
TL;DR: In this paper, the authors employed starburst perfluorinated phenylenes (C60F42) as both hole and exciton block layer, and a hole-transport material 4,4′,4″-tri(N-carbazolyl) triphenylamine as a host for the phosphorescent dopant dye in the emitting layer.
Abstract: One of the keys to highly efficient phosphorescent emission in organic light-emitting devices is to confine triplet excitons generated within the emitting layer. We employ “starburst” perfluorinated phenylenes (C60F42) as a both hole- and exciton-block layer, and a hole-transport material 4,4′,4″-tri(N-carbazolyl) triphenylamine as a host for the phosphorescent dopant dye in the emitting layer. A maximum external quantum efficiency reaches to 19.2%, and keeps over 15% even at high current densities of 10–20 mA/cm2, providing several times the brightness of fluorescent tubes for lighting. The onset voltage of the electroluminescence is as low as 2.4 V and the peak power efficiency is 70–72 lm/W, promising for low-power display devices.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host, achieving a maximum external quantum efficiency of 19.0±1.0 and luminous power efficiency of 60±5 lm/W.
Abstract: We demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate [(ppy)2Ir(acac)] doped into 3-phenyl-4(1′-naphthyl)-5-phenyl-1,2,4-triazole, a maximum external quantum efficiency of (19.0±1.0)% and luminous power efficiency of (60±5) lm/W are achieved. The calculated internal quantum efficiency of (87±7)% is supported by the observed absence of thermally activated nonradiative loss in the photoluminescent efficiency of (ppy)2Ir(acac). Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of (ppy)2Ir(acac) coupled with balanced hole and electron injection, and triplet exciton confinement within the light-emitting layer.

3,302 citations

Journal ArticleDOI
TL;DR: The results indicate that with proper device interface design, perovskite materials are promising candidates for low-cost, high-performance photodetectors.
Abstract: Organic–inorganic hybrid perovskite materials are attracting great interest for their applications in photovoltaics where they have demonstrated excellent efficiency. Here, Dou et al. demonstrate room temperature, solution-processed hybrid perovskite photodetectors with fast response and high detectivity.

2,086 citations

Journal ArticleDOI
TL;DR: A comprehensive review of the literature on electron transport materials (ETMs) used to enhance the performance of organic light-emitting diodes (OLEDs) is presented in this article.
Abstract: A comprehensive review of the literature on electron transport materials (ETMs) used to enhance the performance of organic light-emitting diodes (OLEDs) is presented. The structure−property−performance relationships of many classes of ETMs, both small-molecule- and polymer-based, that have been widely used to improve OLED performance through control of charge injection, transport, and recombination are highlighted. The molecular architecture, electronic structure (electron affinity and ionization potential), thin film processing, thermal stability, morphology, and electron mobility of diverse organic ETMs are discussed and related to their effectiveness in improving OLED performance (efficiency, brightness, and drive voltage). Some issues relating to the experimental procedures for the estimation of relevant material properties such as electron affinity and electron mobility are discussed. The design of multifunctional electroluminescent polymers whereby light emission and electron- and hole-transport pro...

1,527 citations

Journal ArticleDOI
TL;DR: Most present-day semiconductor devices use inorganic crystalline materials, with single-crystalline silicon dominating other materials like GaAs by about a factor of 1000, but organic semiconductors have recently gained much attention and are already broadly applied as photoconductors for copiers and laser printers.
Abstract: Most present-day semiconductor devices use inorganic crystalline materials, with single-crystalline silicon dominating other materials like GaAs by about a factor of 1000. Despite the advantages of single-crystalline inorganic semiconductors like high room-temperature mobility (up to 1000 cm2/(V s)) and high stability, these materials are less suitable for low-cost and large-area applications. Additionally, silicon is an indirect semiconductor and therefore is not well suited for optoelectronic applications like light-emitting diodes. Solar cells from silicon are expensive and require a large amount of energy for their fabrication, leading to a long energy payback time. As an alternative, organic semiconductors have recently gained much attention (for review articles, see refs 1 -3 (OLEDs), ref 4 (organic electronics in general), and refs 5 and 6 (organic solar cells)). Originally, much of the research concentrated on single crystals, which can have mobilities of a few cm2/(V s) at room temperature and even much higher values at low temperature, as shown in the pioneering work of Karl et al.7 However, for practical applications, thinfilm organic semiconductors with disordered morphology, such as evaporated small-molecule compounds or polymers processed from solution, are prevailing. Organic semiconductors are already broadly applied as photoconductors for copiers and laser printers. * Corresponding author. E-mail: leo@iapp.de. Web address: www.iapp.de. 1233 Chem. Rev. 2007, 107, 1233−1271

1,436 citations

Journal ArticleDOI
TL;DR: Blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials.
Abstract: Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.

1,240 citations

References
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Journal ArticleDOI
10 Sep 1998-Nature
TL;DR: In this article, a host material doped with the phosphorescent dye PtOEP (PtOEP II) was used to achieve high energy transfer from both singlet and triplet states.
Abstract: The efficiency of electroluminescent organic light-emitting devices1,2 can be improved by the introduction3 of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the singlet spin states induce fluorescent emission; these represent a small fraction (about 25%) of the total excited-state population (the remainder are triplet states). Phosphorescent dyes, however, offer a means of achieving improved light-emission efficiencies, as emission may result from both singlet and triplet states. Here we report high-efficiency (≳90%) energy transfer from both singlet and triplet states, in a host material doped with the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) (PtOEP). Our doped electroluminescent devices generate saturated red emission with peak external and internal quantum efficiencies of 4% and 23%, respectively. The luminescent efficiencies attainable with phosphorescent dyes may lead to new applications for organic materials. Moreover, our work establishes the utility of PtOEP as a probe of triplet behaviour and energy transfer in organic solid-state systems.

7,023 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host was described.
Abstract: We describe the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host. These devices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A) and 31 lm/W, respectively. At 100 cd/m2, the external quantum and power efficiencies are 7.5% (26 cd/A) and 19 lm/W at an operating voltage of 4.3 V. This performance can be explained by efficient transfer of both singlet and triplet excited states in the host to Ir(ppy)3, leading to a high internal efficiency. In addition, the short phosphorescent decay time of Ir(ppy)3 (<1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m2.

3,594 citations

Journal ArticleDOI
17 Feb 2000-Nature
TL;DR: This work uses the mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as 100%.
Abstract: To obtain the maximum luminous efficiency from an organic material, it is necessary to harness both the spin-symmetric and anti-symmetric molecular excitations (bound electron-hole pairs, or excitons) that result from electrical pumping This is possible if the material is phosphorescent, and high efficiencies have been observed in phosphorescent organic light-emitting devices However, phosphorescence in organic molecules is rare at room temperature The alternative radiative process of fluorescence is more common, but it is approximately 75% less efficient, due to the requirement of spin-symmetry conservation Here, we demonstrate that this deficiency can be overcome by using a phosphorescent sensitizer to excite a fluorescent dye The mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as 100% As an example, we use this approach to nearly quadruple the efficiency of a fluorescent red organic light-emitting device

2,050 citations

Journal ArticleDOI
TL;DR: Baldo et al. as mentioned in this paper showed that the observed decrease in electrophosphorescent intensity in organic light-emitting devices at high current densities is principally due to triplet-triplet annihilation.
Abstract: In the preceding paper, Paper I [Phys Rev B 62, 10 958 (2000)], we studied the formation and diffusion of excitons in several phosphorescent guest-host molecular organic systems In this paper, we demonstrate that the observed decrease in electrophosphorescent intensity in organic light-emitting devices at high current densities [M A Baldo et al, Nature 395, 151 (1998)] is principally due to triplet-triplet annihilation Using parameters extracted from transient phosphorescent decays, we model the quantum efficiency versus current characteristics of electrophosphorescent devices It is found that the increase in luminance observed for phosphors with short excited-state lifetimes is due primarily to reduced triplet-triplet annihilation We also derive an expression for a limiting current density ${(J}_{0})$ above which triplet-triplet annihilation dominates The expression for ${J}_{0}$ allows us to establish the criteria for identifying useful phosphors and to assist in the optimized design of electrophosphorescent molecules and device structures

1,303 citations

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate high-efficiency organic light-emitting devices employing the green electrophosphorescent molecule, fac tris(2-phenylpyridine)iridium [Ir(ppy)3], doped into various electron-transport layer (ETL) hosts.
Abstract: We demonstrate high-efficiency organic light-emitting devices employing the green electrophosphorescent molecule, fac tris(2-phenylpyridine)iridium [Ir(ppy)3], doped into various electron-transport layer (ETL) hosts. Using 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole as the host, a maximum external quantum efficiency (ηext) of 15.4±0.2% and a luminous power efficiency of 40±2 Im/W are achieved. We show that very high internal quantum efficiencies (approaching 100%) are achieved for organic phosphors with low photoluminescence efficiencies due to fundamental differences in the relationship between electroluminescence from triplet and singlet excitons. Based on the performance characteristics of single and double heterostructures, we conclude that exciton formation in Ir(ppy)3 occurs within close proximity to the hole-transport layer/ETL:Ir(ppy)3 interface.

1,088 citations